Hot tube drying



July 10, 1951 w. c. HAM ETAL HOT TUBE DRYING Filed Aug. 31, 1949 INVENZOJPS: William (70 bill/Yale Other/fluent ffifif Messoud .lfiac C.

ATTORNEY Patented July 10, 1951 HOT TUBE DRYING William Oogbill Ham,

house, and Otha Kiachii', Richmond,

Chesterfield County Courtlglen Hitt and Messoud a., Pont de Nemours & Company, W

assignors to E. L dn ilmington, Del.,

a corporation of Delaware Application August 31, 1949, Serial No. 113,292

9 Claims.

This invention relates to the rapid drying of filamentous material and, more particularly, to rapid drying of hydrophilic materials such as regenerated cellulose yarns, filaments, strands, rods, ribbons, tubing and the like on-the-run or while moving from one station to another under low tension.

Previously, drying of yarns and the like as they are being wound has been etlected by passing them through heated chambers or over and around drying rollers but such methods are not conducive to rapid drying or to drying at low tension levels. In pending application Ser. No. 720,030 to Conaway and Hitt, now Patent No. 2,495,053, there is described a method of drying which involves passing the yarn over a hot curved plate. While this method and apparatus is effective in securing both rapid and low tension drying, it is not possible in many circumstances to use this arrangement economically. For instance, with the open plates the yarn is threaded up with some difiiculty and many times the most advantageous arrangement for space and for maximum operator efliciency involves too much alteration.

It is, therefore, an object of this invention to provide an efiective yarn drying tube which permits high operator efliciency and a low-uniform level of tension on the yarn passing therethrough. Other objects will be apparent from the description that follows.

The objects of this invention are accomplished by the use of a hairpin tube drier the two long legs of which are curved on a relatively long radius and are connected at their upper ends by a section bent on a relatively short radius. The yarn is passed through the tube during string-up by a jet means. During winding and drying the tube is heated and a vacuum is applied at a critical point to remove evaporated materials. The insides of the tube preferably have a satin finish. The yarns are effectively dried under low tensions.

Reference is made to the figures which are given only for illustrative purposes and of which Figure 1 is a schematic sketch of the drying operation;

Figure 2 is a detail in section showing the string-up means and Figure 3 is a sectional detail of the vacuum means and the inlet end.

As shown in Figure 1, for convenience, two

- hairpin tubes l and 2 are surrounded by a jacket 3 which may be a steam jacket having an inlet 4 and drains or steam traps 5. More than two tubes may be used per location if one may be employed. The yarn 6 is placed at the mouth of the tube in which it is to be dried and compressed air is forced through a corresponding string-up device 1 at the outlet end. The yarn 6 is sucked through the tube. From the package 8 which is rotated by motor 9 the wet yarn is passed through its respective balloon guide I0 and over the respective guide rollers H and into either tube I or 2. Preferably, the yarn package is directly beneath the tube so that no guides besides the balloon guides are required. At the outlet end after string-up and drying are accomplished, the dried yarn is led over a guide ll through a traverse mechanism l2 and onto a core l3 which is rotated by motor l4 As shown in Figure 3 the inlet end of each tube has a restricted opening. This may be formed in any convenient manner, as, for example, by the use of tapered inserts l5. Situated directly above the restriction is a vacuum take-off device It. This comprises a tubular insert fitting into the drying tube and a suitable orifice plate or connection I! to a vacuum pump (not shown).

The location of the vacuum take-ofi device is critical. As can be seen, the system is substantially closed, the only escape for moisture evaporated from the yarn being at the two open ends. It was found that wet yarn dried in the first portion of its passage through the tube reabsorbed condensed moisture in the last section of the tube. Since the exit leg of the tube and equipment immediately beyond the tube was where condensation and reabsorption of moisture by the yarn took place, it was thought that the application of a slight vacuum at about point A (see Figure 1) would quickly eliminate this difiiculty. This was tried but with no improvement in results. Surprised at this failure, vacuum was next applied at about point B at the topmost point of the drier with improved but unsatisfactory results. It was not until vacuum was applied at point C near the inlet end that efiective drying was obtained and this apparently critical location made the difierence between satisfactorily dried yarn and wet yarn'that was entirely unfit for packaging. Subsequently, it was found that a very slight vacuum at about point C was sufiicient and by sligh is meant only about 4 inches of water column, although a vacuum of up to 12 or 14 inches or more of water column may be used if desired. Application of the vacuum induces a counter-flow of air. This is effective in obtaining maximum drying efiiciency and avoids any desired or only tube as shown in exhaust at the yarn outlet end which would lead to condensation of moisture on machinery and on the dried yarn. V p The string-up jet 1 located at the exit end comprices a tubular insert l8 fltting into the drying Figure 2.. This is connected to a source of high pressure air, say 100 lbs/sq. in. By having the inlet end of the tubestopped down by restriction to an area of less than the inside cross-sectional area of the tube, the yarn, when inserted into the aperture of I5, is quickly drawn through the tube by the suction created by flow of air through 1 and the tube Outlet. The vacuum is turned off during string-up and once that is accomplished, the air is turned off and the vacuum is turned on.

The curvature of the tube is essential for rapid drying at an efficient rate of heat exchange from the tube wall to the wet yarn. The two long legs are bent on a relatively long radius and are connected at their upper ends by a section bent on a relatively short radius. In the specific embodiment shown in Figure 1 the radius of curvature of the two long legs from the lower end to about d-d are bent on a 30 foot radius, although good heating results, with no substantial change in running tension, can be secured if these legs are bent on a radius in the range of from 15-40 feet. The short radius'bend connecting the upper ends of the two legs in the specific illustration is about 2 feet in radius, which short radius is not only desirable to increase the closeness of contact between the yarn and the tube wall but it enables the lower ends of the two legs to be spaced relatively close to give greater ease of operation. The operator, for example, can prepare the package for unwinding, turn on the air jet at the exit end of the tube, get the yarn started through the tube and again be ready to receive the end as it leaves the leg at the wind-up end, at which time he can also shut oif the string-up jet and turn on the vacuum. This upper tube connection bent on a short radius may, of course, be

. 4 Drying of yarns, filaments. strands or the like on the main the drier just described is simply and easily carried out. .After the drier tube has been brought up to the desired temperature. the yarn package is prepared for unwinding by placing it on a spindle to be rotated at low rotational varied somewhat but practically should be maintained in the range of from to 3 or even 5 feet. The over-all length of the tube is about 30 feet, although this length may be changed quite widely depending on the temperature, speed, size of yarn, etc.

In the specific embodiment shown the tube is inch 1. D. and as originally installed it imposed a tension of 15 grams on a 100-denier yarn (dry basis) running therethrough at a speed of 300 yds./min. This tension was excessive for the purpose for which the yarn was intended to be used and it was necessary to reduce this tension to a value below 12 grams per 100-denier yarn.

This was accomplished by sand or grit blasting the inside of the tube to provide the surface therein with a satin-like finish. By thus providing a microscopic pebbly surface in which the hills and valleys are smooth and rounded, yarn tensions were kept below from 8-10 grams per 100-denier or no more than 0.1 gram per denier. With large denier yarns, the effect of the satin finish is less and the finish is not essential, but in all cases the pebbled surface is preferred.

Heat is provided by means of a pressure steam jacket extending from end to end, which in turn is covered with insulating material IS. The temperature normall desired. and obtained on the inside of the drying tube is of the order of speed and thereby eliminate any drag on the yarn being unwound and at the same time imparts a slight twist to the yarn. The string-up jet is opened, the yarn end introduced into the receiving end of the drier and the spindle with the yarn package thereon is released to rotate at low rotational speed. The yarn so'on'starts through the exit end of the tube and after starting it winding and turning off the air jet, the vacuum valve is opened.

' Bobbin-spun, washed, desulfured and doped 100-denier 60-filament regenerated cellulose yarn containing initially about 100% or more of water, based on the air dry weight of the yarn, was passed through the drier at 300 yds./min. windup speed. About 90% or more of the moisture (over and above the equilibrium moisture of about 10%) is removed through the vacuum draw-off. From various other tests made it is believed that about of the removable water is taken out in passing up to the top of the drier and the balance down to a moisture content in the yarn ofabout 10% is removed coming down from the top of the drier. The top section is believed to be the most efficient part of the drier in that more water is removed per foot of travel here than in any other section due largely to the relatively small radius of curvature of this section and also because the water in the yarn has been heated up to near the boiling point by the time it reaches this portion of the drier.

It is indeed surprising that these apparent inconsequential details, such as tube curvature and surface finish on the inside of the tube, play such important roles in the carryin out of this process. It is even more surprising that the location of the vacuum draw-off is so critical and its location may not be varied greatly from the location shown in Figure 1 without noticeably impairing the efiiciency of drying. Indeed, if this vacuum connection is moved up beyond the one-half way point of the first leg, i. e., more than onehalf way from the lower end of this leg to point d, a decided adverse eifect will be brought about. It is, therefore, essential that the location of this vacuum connection be maintained in the lower whether of natural or synthetic origin. Thus,

shaped articles of cellulose, cellulose derivatives, such as cellulose acetate, polyamides, polyacrylonitriles, etc. may be processed in the apparatus. The denier of the yarns or the like may vary widely. Thus, yarns up to 2200 denier or even higher may be dried, although the drying speeds are decreased or the tubes lengthened for these coarser denier yarns. With small denier such as denier-30 filament or denier-60 filament yarn excellent drying is obtained at 312 yards/ min. and with 600 denier-400 filament yarn at 84 yards/min. using temperatures of from C. to C. With coarser deniers temdamage occurs.

The apparatus of this invention has many ad- 1 15 vantages over previously known drying devices. 1

There is more efficient heat utilization and less radiation losses. Drying is accomplished under slightly reduced pressure and this results in a controlled flow of air in the tube with resultant conservation of heat and regulation of vapor discharge. The evaporated water is drawn off in a manner whereby the air conditions around the yarn as well as in the room are controlled. The apparatus is very easily strung-up by means of the air jet. The horseshoe shape of the apparatus makes it possible to bring the string-up and the discharge ends close together thereby conserving space and facilitating operation. Economy in time and labor is effected. Further, the tubular nature of the drier permits ready cleaning in maintaining the proper pebbly surface. A minute period of sand blasting is all that is required to clean and to refinish the surface to regulate the tension imposed on the yarn in the control of yarn shrinkage. Still further} the drying of yarns is accomplished with the use of very low tensions on the yarn. The yarn actually rides on a bed of steam as evidenced by the higher tensions prevailing when a yarn is run through a cold tube. This support not only leads to lower tensions but enables one to leave the yarn in the tube during string-up and package changes for as long as ten minutes without any measurable detrimental effects. Further, the counter-flow of air is highly efiective in obtaining maximum drying efliciency.

Any departure from the above description which conforms to the present invention is in tended to be included within the scope of the claims.

We claim:

1. Apparatus for drying traveling filamentous material comprising a passageway for said ma-- terial formed by two tubular end sections curved on a long radius connected together by a tubular section curved on a short radius; string-up means near one end of said passageway; means for removing vapor near the other end of said passageway; and means for heating said passageway.

2. Apparatus for drying traveling filamentous material comprising a curved tube having two tubular end sections curved on a long radius connected together by a tubular section curved on a short radius; an inlet for said material; an outlet for said material; string-up means near the said outlet; near the said inlet a means for inducing air flow in a direction opposite the direction of travel of said material; and means for heating said tube.

3. Apparatus for drying traveling filamentous material comprising a curved tube having two tubular end sections curved on a radius of from 15 to 40 feet connected together by a tubular section curved on a radius of about 1 to 5 feet; an inlet for said material; an outlet for said material; string-up means near said outlet; near said inlet a means for removing vapor; and means for heating said tube.

4. Apparatus for drying traveling filamentous material. comprising a curved tube having two tubular end sections curved on a radius of from 15 to 40 feet connected together by a tubular section curved on a radius of about 1 to 5 feet; a satin'finish on the interior surfaces of said tube; a constricted inlet for said material; an outlet for said material; near said outlet a jet string-up device; near said inlet a connection to a vacuum; and means for heating said tube.

5. Apparatus in accordance with claim 4 in which said means for heating said tube is a tubular steam jacket surrounding said tube.-

6. Apparatus in accordance with claim 4 in which the said tube has an inside diameter of A; inch.

7. A process for drying filamentous material comprising .passing said material through a curved tube havin two tubular end sections curved on a long radius connected together by a tubular section curved on a short radius; inducing vapor to flow in a direction opposite the direction of travel of said material; heating said tube; and removing the vapor at a point near the entrance point of said material into said tube.

8. A process for drying filamentous material comprising passing said material through a curved tube having two tubular end sections curved on a long radius connected together by a tubular section curved on a short radius, said material being initially jetted through said tube; inducing vapor to flow in a direction opposite the direction of travel of said material; heating said tube; and removing the vapor at a point near the entrance point of said material into said tube.

9. A process for dryin filamentous material comprising passing said material, under a tension of no more than 0.1 gram per denier, through a curved tube having two tubular end sections curved on radius of from 15 to 40 feet connected together by a tubular section curved on a radius of about 1 to 5 feet; inducing vapor to flow in a direction opposite the direction of travel of said material; heating the said tube; and removing the vapor at a point near the entrance point of said material into said tube.

WILLIAM COGBILL HAM. OTHA ALLEN Hrr'r. MESSOUD moms.

REFERENCES CITED Conaway et a1. Jan. 17, 1950 

